Power allocation scheme for DMT-based modems employing simplex transmission

ABSTRACT

The present invention provides a method, apparatus and computer readable medium for allocation of an available power to Discrete Multi-Tone (DMT) frequency tones in a DMT-based Digital Subscriber Line (DSL) modem. In one embodiment, the method includes the steps of: initializing the DMT-based DSL modem by calculating aggregate values of channel attenuation, noise power, and power mask; pre-filtering to flag noisy bins that are unable to support a minimum number of bits with the maximum power available for transmission in a bin; and using a repeated-bisection splitting scheme to allocate the available power substantially optimally among a plurality of bands for DMT frequency tones.

This application is a continuation of prior application Ser. No.11/235,729 filed Sep. 26, 2005, now U.S. Pat. No. 7,254,166 which is acontinuation of prior application Ser. No. 09/771,181, filed Jan. 26,2001 which issued as U.S. Pat. No. 6,973,122, both of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to simplex transmission ofsignals in a multicarrier-based modem system, and more particularly to amethod and system for allocating information bits when the power needsto be assigned for Discrete Multi-Tone (DMT) transmission.

BACKGROUND OF THE INVENTION

Digital Subscriber Line (DSL) technology greatly increases the digitalcapacity of an ordinary telephone line, allowing much more informationto be channeled into a home or office. The speed that a DSL modem canachieve is based on the distance between the home or office and thecentral office. Symmetric DSL (SDSL) utilizes a single twisted pair andis typically used for short connections that need high speed in bothdirections. High Bit Rate DSL (HDSL) is a symmetric technology that usestwo cable pairs and may achieve usable transmission to 12,000 feet Eachtwisted pair may be used to provide T1 transmission, but the lines maynot be shared with analog phones. HDSL-2 needs only one cable pair andsupports a distance of 18,000 feet. SDSL utilizes only one cable pairand may be used with adaptive rates from 144 Kbps to 1.5 Mbps. The DSLtechnology provides “always-on” operation.

Asymmetric DSL (ADSL), which uses frequencies that are higher thanvoice, shares telephone lines and may be used to access the Internet.For ADSL, a Plain Old Telephone System (POTS) splitter generally must beinstalled at the user end to separate the voice frequencies and the ADSLfrequencies. The G.lite version of ADSL, also known as the ADSL lite,Universal ADSL or splitterless ADSL, gets around the splitterrequirement by having all phones plug into low-pass filters that removethe ADSL high frequencies from the voice transmissions. ADSL isavailable in two modulation schemes: the Discrete Multi-tone (DMT) orCarrierless Amplitude Phase (CAP).

In DMT-based DSL modems, the selected bandwidth of 1.104 MHz is dividedinto bins and the data bits are used for Quadrature Amplitude Modulationin each bin. During the initialization period, a channel SNR estimationphase is employed to transmit a known pseudo-random noise (PRN) sequencewhile the receiver computes the channel characteristics from thereceived signal. The characteristics are computed in the form of ag_(k)·N_(k) ⁻¹ ratio, where g_(k) is the channel gain (attenuation,|H(k)|²) in frequency band k, and N_(k) is the noise power in band k.Prior art has disclosed a number of algorithms for determining the powerdistribution across the full frequency bandwidth for maximum data rate.The optimum approach for Additive White Gaussian Noise (AWGN), has beenproved to be a ‘water pouring’ algorithm of power distribution, wherethe g_(k)·N_(k) ⁻¹ profile is considered to be equivalent to the‘terrain’ and the available power budget is likened to ‘water that ispoured’ on the terrain. In this analogy, the water depth at position kis equivalent to the power allocated to the frequency bin k.

The following analysis provides a brief description of this approach. Asis known to those skilled in the art, the relationship between thenumber of bits in a frequency bin and the power needed to transmit thatnumber of bits, for a specified bit error rate (BER) at the receiver forwhich g_(k)·N_(k) ⁻¹ is the measured channel characteristic, is given bythe following expression:

$\begin{matrix}\begin{matrix}{b_{k} = {\log_{2}\lbrack {1 + \frac{3 \cdot g_{k}^{\prime} \cdot E_{k}}{K \cdot ( N_{k} )}} \rbrack}} & {k = {1\mspace{14mu}\ldots\mspace{14mu} 256}}\end{matrix} & {{Eq}.\mspace{14mu} 1}\end{matrix}$whereb_(k)=No. of bits in frequency bin k

E_(k)=Power required in bin k to transmit the b_(k) bits

$\frac{g_{k}^{\prime}}{N_{k}} = {{Measured}\mspace{14mu}{channel}\mspace{20mu}{attenuation}{\mspace{11mu}\;}{to}\mspace{14mu}{noise}\mspace{14mu}{power}\mspace{14mu}{ratio}\mspace{14mu}{in}\mspace{14mu}{bin}\mspace{14mu} k}$N_(k)=Noise power in bin k

$K = {{\lbrack {Q^{- 1}( \frac{P_{e}}{N_{e}} )} \rbrack^{2}\mspace{14mu}{where}\mspace{14mu} 2} \leq \lbrack {N_{e} = {4 \cdot ( {1 - \frac{1}{\sqrt{2^{b_{1}}}}} )}} \rbrack \leq {4\mspace{14mu}{for}\mspace{14mu} 2} \leq {b_{k}.}}$Given the expression in Eq. 1, the power needed to transmit b_(k) bitsin bin k can be obtained by inverting the expression by ignoring thedependence of N_(e) on b_(k). (Prior art has shown that approximatingN_(e) by a constant between 2 and 4 has a negligible effect on theoverall data capacity.)

$E_{k} = {{\frac{KN}{3g_{k}^{\prime}}( {2^{b_{k}} - 1} )} = {{\frac{N}{g_{k}}( {2^{b_{k}} - 1} )\mspace{14mu}{where}\mspace{14mu} g_{k}} = \frac{3g^{\prime}}{K}}}$The problem of power allocation consists of distributing the availablepower budget over the 256-bins so that the capacity as defined by

$\sum\limits_{k = 1}^{256}\; b_{k}$is maximized. The allocation must be performed within constraints of theDSL modems that are subject to a power mask constraint that limits themaximum power that may be allocated to each bin.

The solution to the 2-tone power allocation problem is known in the art.The available power is distributed optimally over two bins to maximizethe 2-bin capacity of b₁+b₂. In order to perform the 256-bin powerallocation, the prior art proposes an iterative approach to solve the“water-pouring” problem. However, such a solution for the 256-bin powerallocation results in noisy bins. Thus, there is a need for a method,system and computer medium for assigning data bits to bins for simplextransmission while minimizing noise.

SUMMARY OF THE INVENTION

The present invention provides a method, apparatus, computer readablemedium and modem for allocation of an available power to DiscreteMulti-Tone (DMT) frequency tones in a DMT-based Digital Subscriber Line(DSL) modem. The steps typically include: (1) initializing the DMT-basedDSL modem by calculating aggregate values of channel attenuation, noisepower, and power mask; (2) pre-filtering to flag noisy bins that areunable to support a minimum number of bits with a maximum poweravailable for transmission in a bin; and (3) using a repeated-bisectionsplitting scheme to allocate the available power substantially optimallyamong a plurality of bands for DMT frequency tones, where bins flaggedin the pre-filtering step are excluded.

In one embodiment, the repeated-bisection splitting scheme may includethe steps of: splitting the available power optimally between the lowerand the upper halves of a 1.104-MHz bandwidth to form two powerfractions for two substantially 552 KHz wide bands; splitting each ofthe two power fractions substantially optimally between two halves ofeach of the substantially 552 KHz wide bands to form four powerfractions for four substantially 276 KHz wide bands; splitting each ofthe four power fractions optimally between two halves of each of thefour substantially 276 KHz wide bands to form eight power fractions foreight substantially 138 KHz wide bands; splitting each of the eightpower fractions optimally between two halves of each of the eightsubstantially 138 KHz wide bands to form sixteen power fractions forsixteen substantially 69 KHz wide bands; splitting each of the sixteenpower fractions optimally between two halves of each of the sixteensubstantially 69 KHz wide bands to form thirty-two power fractions forthirty-two substantially 34.5 KHz wide bands; splitting each of thethirty-two power fractions optimally between two halves of each of thethirty-two substantially 34.5 KHz wide bands to form sixty-four powerfractions for sixty-four substantially 17.25 KHz wide bands; splittingeach of the sixty-four power fractions optimally between two halves ofeach of the sixty-four 17.25 KHz wide bands to form one hundred twentyeight power fractions for one hundred twenty eight substantially 8.625KHz wide bands; and splitting each of the one hundred twenty eight powerfractions optimally between two halves of each of the one hundred twentyeight, 8.625 KHz wide bands to form two hundred fifty six powerfractions to form two hundred fifty six substantially 4.3125 KHz widebands.

The initializing step may include calculating aggregate parametersneeded for the splitting steps while excluding bins flagged in thepre-filtering step.

Each of 2^(f) elements of a noise power vector to be used at step-j maybe calculated as a sum of noise power values in bins aggregated for thestep-j, where j=1, . . . , 8. Each of 2^(f) elements of a channelattenuation vector that is to be used at step-j may be calculated as anaverage of channel attenuation values in bins aggregated for step-j,where j=1, . . . , 8. Each of 2^(j) elements of a power mask vector thatis to be used at step-j may be calculated as a sum of power mask valuesin bins aggregated for step-j, where j=1, . . . , 8.

The available power may be allocated to 2^(n) tones where n is apreselected integer. Here, initializing includes calculating aggregateparameter values of channel attenuation, noise power, and power mask forn subsequent steps.

The apparatus of the present invention allocates the available powerbudget to a plurality of Discrete Multi-Tone (DMT) frequency tones usinga repeated-bisection of power scheme to partition the available powerover the plurality of DMT frequency tones in a DMT-based DigitalSubscriber Line (DSL) modem. The apparatus includes an initializationunit, a pre-filtering unit, and a repeated-bisection power splitting andallocation unit. The initialization unit initializes the DMT-based DSLmodem by calculating aggregate parameter values of channel attenuation,noise power, and power mask. The pre-filtering unit is coupled to theinitialization unit and is used for pre-filtering to flag noisy binsthat are unable to support a minimum number of bits with a maximum poweravailable for transmission in a bin. The pre-filtering step is utilizedto ensure that narrow-band energy from radio sources, power lines, andother line-spectrum-producing interferers does not distort thepower-allocation process by “wasting” power in bins which overlay theseinterferers. The repeated-bisection power splitting and allocation unitis coupled to the pre-filtering unit and is used for implementing therepeated bisection of power scheme of the invention to allocateavailable power substantially optimally among a plurality of bands forDMT frequency tones, where bins flagged by the pre-filtering unit areexcluded. Where desired, the initialization unit may receivenotification of the flagged noisy bins from the pre-filtering unit andexclude the flagged noisy bins.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary of the invention, as well as the followingdetailed description of preferred embodiments, is better understood whenread in conjunction with the accompanying drawings, which are includedby way of example, and not by way of limitation with regard to theclaimed invention.

FIG. 1 is a schematic representation of steps, splits and frequencybands in a multi-tone power splitting scheme in accordance with thepresent invention.

FIG. 2 is a flow diagram of one embodiment of steps in accordance withthe method of the present invention.

FIG. 3 is a block diagram of a modem having an apparatus for allocationof an available power to Discrete Multi-Tone frequency tones in aDiscrete Multi-Tone frequency-based Digital Subscriber Line inaccordance with the present invention.

FIG. 4 is a flow chart showing two embodiments of steps in accordancewith the method of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention utilizes a “repeated-bisection” scheme to extendthe 2-bin solution to 256-bins instead of using the iterative schemesuggested in the prior art. The prior art considers the simple case inwhich the power is to be distributed over two bins. The two-bincapacity, b₁+b₂ is maximized with respect to the power to be allocatedto bin-1 as (E_(r)), when the power is E and the power to be allocatedto bin-2 is E-E_(r). It can be shown that the optimum power allocationto bin 1 is given by the following expression.

$\begin{matrix}{E_{r} = {\frac{1}{2}( {E + {N_{2} \cdot g_{2}^{- 1}} - {N_{1} \cdot g_{1}^{- 1}}} )}} & {{Eq}.\mspace{14mu} 2}\end{matrix}$This solution is derived for the two-tone simplex transmission. It isalso the water-filling solution, e.g., if the noise power andattenuation coefficients in the two bins are equal, the two terms canceleach other and the power is divided equally between the two bins.Similarly, the smaller the ratio of noise power to attenuationcoefficient is in bin 1, the larger the value of E_(r) is, which inturn, allocates greater power to bin 1. The above expression may besimplified by denoting M_(i)=N_(i)·g_(i) ⁻¹ for i=1,2 and t₂₁=M₂ ⁻¹−M₁⁻¹:E _(r)=0.5·(E+t ₂₁) and E−E _(r)=0.5·(E−t ₂₁)=0.5·(E+t ₂₁)  Eq. 3

Discrete Multi-tone-based Digital Subscriber Loop (DSL) modems require ascheme for allocating bits and power to the discrete tones during theinitialization period. As shown in FIG. 2, the initialization parametersare computed 202, and pre-filtering is used to remove bins that cannotsupport the minimum number of bits 204. Then the repeated-bisectionsplitting scheme of the present invention partitions available powerover all the frequency bins to which power needs to be assigned forDMT-transmission 206, 208, 210, 210, 212, 214, 216, 218: The powerallocation is performed with the objective of maximizing the total datarate.

Extension to Multi-Bins

In the present invention, a repeated bisection scheme is used forextending the two-tone solution to the 256-tone case. The schemeoperates by first bisecting the 1.104 Mz band into halves to solve thefirst ‘2-tone’ problem. In the second split, two problems, each adifferent 2-tone problem, are solved. In split 3, four problems, each adifferent 2-tone problem, are solved. This process of progressivelysplitting each band in halves is continued for 8 splits, until power isallocated to each of the 256 bins. The repeated bisection scheme 206,208, 210, 210, 212, 214, 216, 218 is shown schematically in FIGS. 1 and2. The number of bands that are produced as a result of split-i is equalto 2^(i) and the bandwidth of each band at split-i is equal to

$\frac{1104}{2^{l}}\mspace{14mu}{{KHz}.}$Thus, at split 1, each band is 552 KHz wide and at the 8^(th) split,each band corresponds to the DMT frequency bin. FIG. 1 also shows thenumber of 2-tone solutions that must be computed at each split. Atsplit-1, one 2-tone solution generates the partition of the budgetedpower over each of two 552 KHz frequency bands. Each of these two powerfractions is split into two parts in split-2 to yield power allocationsto four 276 KHz frequency bands. FIG. 1 shows that the maximum number of2-tone solutions that may have to be computed is equal to 255. Thefollowing explains the procedure for calculating the values of thechannel attenuation and noise PSD profiles at each split.

Pre-Filtering to Eliminate Noisy Bins

In a pre-filtering step, the invention provides for calculating thenumber of bits that can be received in a bin with the desired bit errorrate (BER), when the tone is transmitted with a power level that isequal to that specified by the power mask value at the frequency bin. Ifthe calculated value is less than the minimum number of bits that can beallocated to that bin, then the bin is flagged for exclusion from thesubsequent power allocation steps.

Input Power at Each Split

In the first split, the power budgets allocated are allocated to the twohalves. For example, the 0.1-Watt budgeted power would be split betweenthe upper and the lower halves of the entire 1.104 MHz band.

In the second split, the input power to each of the two portions wouldbe the partial power allocated to the corresponding half-band in split1. For example, if 75 mWatt is assigned to the lower half-band and therest of the 25 mWatts is allocated to the upper half-band, then thepower inputs to the two 2-tone portions is 75 and 25 mWatts,respectively.

In the third split, the power input to each of the four portions is thepartial power allocated to the corresponding quarter-band in split 2.

As shown in FIG. 1, step-8 consists of performing 128 solutions of the2-bin allocation portions. Thus, split 8 is the only part of the schemethat uses the normal DMT bins. All of the earlier 7 steps require systemparameters for progressively wider frequency bands. In fact, the ‘tone’to which power is allocated in step-i (i=1 . . . 8) is of a bandwidththat corresponds to that of 2^(8-i) frequency bins. Hence, theappropriate channel parameters must be calculated for each step.

-   -   No. of 2-tone solutions at step-i=2^(i−1)    -   No. of frequency bands produced at step i=2^(i)    -   j Δ Band Index at step-i=1 . . . 2^(i)

Noise Power at each Split

Noise power in band index j should be the total noise power in thatband. If N_(k) represents the noise power in bin k (k=1 . . . 256), thenthe noise power in band j at step i may be calculated as follows andstored for use in the 7-steps of the band-splitting scheme. Thecalculation of the integrated noise power values needs to be performedjust once, and it adds 254-array elements to the storage requirement.Note that the summations for average noise calculation are performedover only those bins that can support at least the minimum number ofbits with the maximum power that can be allocated to one bin asdetermined in the pre-filtering step above.

$\begin{matrix}{{{N( {i,j} )} = {\sum\limits_{k \in {band}_{j}}\;{N_{k}\mspace{14mu}{where}}}},{k = {1\mspace{14mu}\ldots\mspace{14mu} 2^{i}}}} & {{Eq}.\mspace{14mu} 4}\end{matrix}$

Channel Attenuation Parameters at each Split

The channel attenuation coefficient in bin-k in each band, g_(k), is theaverage value for the band. The summations for the calculation ofaverage channel attenuation are performed over only those bins that werenot excluded by the pre-filtering step.

$\begin{matrix}{{g( {i,j} )} = {{{\frac{1}{2^{B - 1}} \cdot ( {\sum\limits_{k \in {band}_{j}}g_{k}} )}\mspace{14mu}{where}\mspace{14mu} j} = {1\mspace{14mu}\ldots\mspace{14mu} 2^{i}}}} & {{Eq}.\mspace{14mu} 5}\end{matrix}$

Power mask Constraint at each Split

The power mask constraint may be applied by calculating the implied maskconstraint for each of the wider bands used in splits 1 through 7. Powermask in band index j should be the total power mask in that band. IfPmask_(k) represent the power mask values in bin k (k=1 . . . 256), thenthe power mask in band j at step i can be calculated and stored for usein the 7-steps of the band-splitting scheme. The calculation of theintegrated power mask values needs to be performed just once, and itadds 254-array elements to the storage requirement. The ADSL parametersare such that the total integrated power mask exceeds the power budget.Hence, a signal is not intended to be as large as to reach the powermask at all the frequencies. Therefore, the integrated values of thepower mask for the wider bins are compared with the total power budgetand the integrated power mask is set as the minimum of the integratedvalue and the total power budget.

${{Pmask}( {i,j} )} = {{{\min( {{\sum\limits_{k \in {band}_{j}}{Pmask}_{k}},P_{budget}} )}\mspace{14mu}{where}\mspace{14mu} j} = {1\mspace{14mu}\ldots\mspace{11mu} 2^{i}}}$

FIG. 3 is a block diagram of a modem 302 having an apparatus 304 forallocating an available power to a plurality of Discrete Multi-Tone(DMT) frequency tones using a repeated-bisection of power scheme topartition the available power over the plurality of DMT frequency tonesin a DMT-based Digital Subscriber Line (DSL) in accordance with thepresent invention. The apparatus 304 includes an initialization unit306, a pre-filtering unit 308 and a repeated-bisection power splittingand allocation unit 310. The initialization unit 304 is used forinitializing the DMT-based DSL modem by calculating aggregate parametervalues of channel attenuation, noise power, and power mask. Thepre-filtering unit 308 is coupled to the initialization unit 306 and isused for pre-filtering to flag noisy bins that are unable to support aminimum number of bits with a maximum power available for transmissionin a bin. The repeated-bisection power splitting and allocation unit 310is coupled to the pre-filtering unit 308 and is utilized for using therepeated-bisection of power scheme to allocate the available powersubstantially optimally among a plurality of bands for DMT frequencytones. As shown by the solid lines, the available power may be sent tothe initialization unit 306, which sends its output to the pre-filteringunit 308, which sends its output to the repeated-bisection powersplitting and allocation unit 310. The actions taken in the units are asdescribed below in the corresponding method steps.

In one embodiment, the repeated-bisection splitting unit 310 mayimplement the repeated-bisection of power scheme by: splitting theavailable power optimally between the lower and the upper halves of a1.104-MHz bandwidth to form two power fractions for two substantially552 KHz wide bands; splitting each of the two power fractionssubstantially optimally between two halves of each of the substantially552 KHz wide bands to form four power fractions for four substantially276 KHz wide bands; splitting each of the four power fractions optimallybetween two halves of each of the four substantially 276 KHz wide bandsto form eight power fractions for eight substantially 138 KHz widebands; splitting each of the eight power fractions optimally between twohalves of each of the eight substantially 138 KHz wide bands to formsixteen power fractions for sixteen substantially 69 KHz wide bands;splitting each of the sixteen power fractions optimally between twohalves of each of the sixteen substantially 69 KHz wide bands to formthirty-two power fractions for thirty-two substantially 34.5 KIz widebands; splitting each of the thirty-two power fractions optimallybetween two halves of each of the thirty-two substantially 34.5 KHz widebands to form sixty-four power fractions for sixty-four substantially17.25 KHz wide bands; splitting each of the sixty-four power fractionsoptimally between two halves of each of the sixty-four 17.25 KHz widebands to form one hundred twenty eight power fractions for one hundredtwenty eight substantially 8.625 KHz wide bands; and splitting each ofthe one hundred twenty eight power fractions optimally between twohalves of each of the one hundred twenty eight, 8.625 KHz wide bands toform two hundred fifty six power fractions to form two hundred fifty sixsubstantially 4.3125 KHz wide bands.

Alternatively, the available power may be sent to the pre-filtering unit308 first, whose output is sent to the initialization unit 306, and theoutput of the initialization unit may be sent to the repeated-bisectionpower splitting and allocation unit 310. In this embodiment, theinitialization unit 306 is coupled to the pre-filtering unit 308 whichreceives the available power, such that the initialization unit 306receives notification of the bins that are flagged, and then calculatesaggregate parameter values needed to implement the repeated-bisection ofpower scheme and excludes bins flagged by the pre-filtering unit.

In one embodiment, each of 2^(j) elements of a noise power vector to beused at step-j of the repeated-bisection of power scheme may becalculated as a sum of noise power values in bins aggregated for thestep-j, where j=1, . . . , 8. Similarly, each of 2^(j) elements of achannel attenuation vector that is to be used at step-j of therepeated-bisection of power scheme may be calculated as an average ofchannel attenuation values in bins aggregated for step-j, where j=1, . .. , 8. Also, each of 2^(j) elements of a power mask vector that is to beused at step-j of the repeated-bisection of power scheme may becalculated as a sum of power mask values in bins aggregated for step-j,where j=1, . . . , 8.

The available power may be selected to be allocated to 2^(n) tones wheren is a preselected integer. Typically, in this embodiment, theinitialization unit 306 initializes the modem by calculating aggregateparameter values of channel attenuation, noise power, and power mask forn subsequent steps.

FIG. 4 shows a method for allocation of an available power to DiscreteMulti-Tone (DMT) frequency tones in a DMT-based Digital Subscriber Line(DSL) modem in accordance with the present invention. The methodtypically includes the steps of: initializing 402 the DMT-based DSLmodem by calculating aggregate values of channel attenuation, noisepower, and power mask; pre-filtering 404 to flag noisy bins that areunable to support a minimum number of bits with a maximum poweravailable for transmission in a bin; and using a repeated-bisectionsplitting scheme 406 to allocate the available power substantiallyoptimally among a plurality of bands for DMT frequency tones, wherein,where bins flagged in the pre-filtering process and not yet excluded areexcluded by the scheme.

The method may implement the repeated-bisection splitting scheme by:splitting the available power optimally between the lower and the upperhalves of a 1.104-MHz bandwidth to form two power fractions for twosubstantially 552 KHz wide bands; splitting each of the two powerfractions substantially optimally between two halves of each of thesubstantially 552 KHz wide bands to form four power fractions for foursubstantially 276 KHz wide bands; splitting each of the four powerfractions optimally between two halves of each of the four substantially276 KHz wide bands to form eight power fractions for eight substantially138 KHz wide bands; splitting each of the eight power fractionsoptimally between two halves of each of the eight substantially 138 KHzwide bands to form sixteen power fractions for sixteen substantially 69KHz wide bands; splitting each of the sixteen power fractions optimallybetween two halves of each of the sixteen substantially 69 KHz widebands to form thirty-two power fractions for thirty-two substantially34.5 KHz wide bands; splitting each of the thirty-two power fractionsoptimally between two halves of each of the thirty-two substantially34.5 KHz wide bands to form sixty-four power fractions for sixty-foursubstantially 17.25 KHz wide bands; splitting each of the sixty-fourpower fractions optimally between two halves of each of the sixty-four17.25 KHz wide bands to form one hundred twenty eight power fractionsfor one hundred twenty eight substantially 8.625 KHz wide bands; andsplitting each of the one hundred twenty eight power fractions optimallybetween two halves of each of the one hundred twenty eight, 8.625 KHzwide bands to form two hundred fifty six power fractions to form twohundred fifty six substantially 4.3125 KHz wide bands.

Where the pre-filtering step 404 precedes the initializing step 402(dashed lines), the initializing step 402 may provide for calculatingaggregate parameters needed while excluding noisy bins that are flaggedas unable to support a minimum number of bits with a maximum poweravailable for transmission in a bin.

Each of 2^(j) elements of a noise power vector to be used at step-j maybe calculated as a sum of noise power values in bins aggregated for thestep-j, where j=1, . . . , 8. Also, each of 2^(j) elements of a channelattenuation vector that is to be used at step-j may be calculated as anaverage of channel attenuation values in bins aggregated for step-j,where j=1, . . . , 8. In addition, each of 2^(j) elements of a powermask vector that is to be used at step-j may be calculated as a sum ofpower mask values in bins aggregated for step-j, where j=1, . . . , 8.

Generally, the available power is allocated to 2^(n) tones where n is apreselected integer. Initializing typically includes calculatingaggregate parameter values of channel attenuation, noise power, andpower mask for n subsequent steps.

Clearly, the method of the invention may be implemented by digitalsignal processor, a microprocessor, a general processor, or othercircuitry arranged to implement the steps of the method.

The present invention may be implemented by a computer readable mediumsuch as, for example, a memory, computer disk, or the like, havingcomputer-executable instructions for allocation of an available power toDiscrete Multi-Tone (DMT) frequency tones in a DMT-based DigitalSubscriber Line (DSL) modem, wherein the computer-executableinstructions include the steps of: initializing the modem by calculatingaggregate values of channel attenuation, noise power, and power mask;pre-filtering to flag noisy bins that are unable to support a minimumnumber of bits with a maximum power available for transmission in a bin;and using a repeated-bisection splitting scheme to allocate theavailable power substantially optimally among a plurality of bands forDMT frequency tones. The exclusion of the flagged bins may beaccomplished in the initializing step or, alternatively, in the step ofusing the repeated-bisection splitting scheme. Where desired, therepeated-bisection splitting scheme may include the steps enumeratedabove.

Each of 2^(j) elements of a noise power vector to be used at step-j ofthe repeated-bisection splitting scheme may be calculated as a sum ofnoise power values in bins aggregated for the step-j, where j=1, . . . ,8. Similarly, each of 2^(j) elements of a channel attenuation vectorthat is to be used at step-j of the repeated-bisection splitting schememay be calculated as an average of channel attenuation values in binsaggregated for step-j, where j=1, . . . , 8. Also, each of 2^(j)elements of a power mask vector that is to be used at step-j of therepeated-bisection splitting scheme may be calculated as a sum of powermask values in bins aggregated for step-j, where j=1, . . . , 8. Theavailable power is generally allocated to 2^(n) tones where n is apreselected integer. Initializing typically includes calculatingaggregate parameter values of channel attenuation, noise power, andpower mask for n subsequent steps.

Although the present invention has been described in relation toparticular preferred embodiments thereof, many variations, equivalents,modifications and other uses will become apparent to those skilled inthe art. It is preferred, therefore, that the present invention belimited not by the specific disclosure herein, but only by the appendedclaims.

1. A method for allocating an available amount of power to a pluralityof Discrete Multi-Tone (DMT) frequency tones, each tone in saidplurality of tones corresponding to a bin of predetermined bandwidth ina plurality of bins of predetermined bandwidth, said method comprising:allocating said available amount of power to said plurality of tonesusing a repeated bisection scheme; identifying at least a first bin ofpredetermined bandwidth in said plurality of bins of predeterminedbandwidth that is unable to receive a predetermined minimum number ofbits using a predetermined portion of said available amount of power;and allocating said available amount of power to all bins in saidplurality of bins except said at least a first bin of predeterminedbandwidth.
 2. The method of claim 1 wherein said step of identifyingcomprises: calculating a first number of bits that can be received insaid at least a first bin of predetermined bandwidth with less than adesired bit error rate; and comparing said first number of bits to saidpredetermined minimum number of bits.
 3. The method of claim 2 whereinsaid available amount of power is a power level of a tone correspondingto said at least a first bin of predetermined bandwidth.
 4. An apparatusfor allocating an available amount of power to a plurality of DiscreteMulti-Tone (DMT) frequency tones, each tone in said plurality of tonescorresponding to a bin of predetermined bandwidth in a plurality of binsof predetermined bandwidth, said apparatus comprising: a pre-filteringunit configured to identify at least a first bin of predeterminedbandwidth in said plurality of bins of predetermined bandwidth that isunable to receive a predetermined minimum number of bits using apredetermined portion of said available amount of power; and arepeated-bisection power splitting and allocation unit configured toallocate said available amount of power to said plurality of tones usinga repeated bisection scheme and allocate said available amount of powerto all bins in said plurality of bins except said at least a first binof predetermined bandwidth.
 5. A computer readable medium comprisingcomputer program instructions which, when executed by a processor,define steps for allocating an available amount of power to a pluralityof Discrete Multi-Tone (DMT) frequency tones, each tone in saidplurality of tones corresponding to a bin of predetermined bandwidth ina plurality of bins of predetermined bandwidth, said steps comprising:allocating said available amount of power to said plurality of tonesusing a repeated bisection scheme; identifying at least a first bin ofpredetermined bandwidth in said plurality of bins of predeterminedbandwidth that is unable to receive a predetermined minimum number ofbits using a portion of said available amount of power; and allocatingsaid available amount of power to all bins in said plurality of binsexcept said at least a first bin of predetermined bandwidth.